GB2086726A - Method for sterilizing masonry - Google Patents

Abstract

By establishing in at least one cavity in masonry a fused body of biocidal material including boric oxide, said fused body being shaped to fit said cavity, masonry can be sterilised in order to prevent, or reduce the incidence of, organism growth induced by the presence of moisture.

Description

SPECIFICATION Method for sterilizing masonry This invention relates to the sterilisation of masonry, in particular in order to prevent, or reduce the incidence of, organism growth induced by the presence of moisture.

Dampness in masonry, for example rising damp, commonly supports organic growth, for example of moulds or fungi. Such organic growth can cause considerable damage, for example to the masonry, or timber associated therewith as by rotting, or to decorations such as wallpaper. By way of illustration the dry rot fungus Merulius (Serpula) lachrymans, which can have a disastrous effect on wood, has a mycelium which can infest masonry and cause dry rot in woodwork, such as door or window frames, in contact with masonry. It is known to sterilise masonry in order to prevent or inhibit such organic growth by inserting sterilant materials into cavities in the masonry, but known sterilant materials do not meet all of the required criteria.For example, a most desirable characteristic of a sterilent for masonry is that it should be highly effective against fungi without being harmful to humans and domestic animals that might come into contact with treated masonry. A sterilant material must also be safe and easy to handle and to install, must have a long active life, and must not adversely affect the masonry, in particular by increasing its water content. Furthermore, the efficacy of a sterilant should not be adversely affected by chemicals, such as lime, contained in masonry.

We have found that boric oxide, B203, is a most effective sterilant, or biocidal, material for use in the treatment of masonry. According to the invention we provide a method of sterilising masonry in order to prevent, or reduce the incidence of, organism growth induced by the presence of moisture, which method comprises establishing in at least one cavity in the masonry a fused body of biocidal material including boric oxide, said fused body being shaped to fit said cavity.

The fused bodies to be used in accordance with the invention in the sterilisation of masonry are described in U.K. Patent Application 78 26210 (Published Specification 2008640A), which also describes the use of the fused bodies in the preservation of timber.

The fused body is not composed of discrete particles of (fused) boric oxide or other sterilant material but is a single element. Whereas a compacted but unfused body of boric oxide dissolves fairly rapidly in the moisture found in masonry, a fused body dissolves more slowly and only in response to the demands of the particular environment in which it is used, so giving protection over a longer period.

The fused body may contain other materials as well, and these may either be fused with the boric oxide or be present as discrete particles in a fused matrix of boric oxide. These other materials will usually be oxides which effect one or both of the following: (i) control of the rate of solution in water, and (ii) enhancement of the sterilant power of the boric acid.

Typical examples of materials achieving (i) are alkali metal oxides (which increase the rate of solution) and alkaline earth metal or silicon oxides (which reduce the rate of solution). When the fused body comprises both an alkali metal oxide and boric oxide they are preferably in combined form as an alkali metal borate, such as a sodium borate having the approximate composition Na2B8O'3 (anhydrous "POLYBOR' '-Registered Trade Mark). Silica is especially valuable for retarding solution of boric oxide.

Typical examples of materials achieving (ii) are copper oxide, tin oxide, zinc oxide; some fungi are controlled more effectively by copper oxide or one of the other metal oxides with boric acid.

The fused body is shaped to fit a correspondingly shaped cavity in the masonry. The most convenient form of shaped body is a rod or cylinder, e.g. a circular cylinder, having a length longer than its maximum width; alternative forms include blocks, pellets and bullets. These shaped bodies can be made by casting or otherwise shaping the sterilant material in molten state or by moulding and compacting particulate materials in a mould and then fusing by heat to provide a monolithic structure. Preferably molten sterilant material is cast into a mould to provide the shaped body.

After a fused body of sterilant material has been inserted into a cavity in the masonry, for example in brickwork or in a mortar course between adjacent layers of bricks, the filled cavity can be capped to prevent direct ingress of moisture.

Advantageously there is formed in the masonry a plurality of cavities in each of which is inserted at least one fused body. The cavities clearly should be so placed that the fused bodies will come into contact with water entering the masonry, as by rising damp for example. The rate at which sterilant material is made available is determined not only by the formulation used, as explained above, but also by the rate at which water enters the masonry and contacts a fused body. For a given formulation the rate of supply of the sterilant material will be greater the greater is the amount of water entering the masonry and the more would otherwise have been the growth of the undesirable organism. The rate of supply of the sterilant material is therefore self-regulating and according to need or demand.It is not necessary, as with known materials, to dissipate the sterilant material throughout the masonry to areas in which it is not neded, there being no moisture in such areas. Also, being fused, the body is of high density, so that the volume occupied by a given weight of the sterilant material is less than for a particulate material and the cavity into which the fused body is inserted can be smaller. It is of course cheaper and quicker to drill a small hole than a large one. Moreover, the fused material dissolves more slowly in moisture in the masonry than does the same material in particulate form, and yet can still dissolve fast enough to maintain the desired concentration of biocide in the area of masonry most subject to fungal growth due to the presence of moisture.

Boric oxide dissolves in moisture of the masonry to form boric acid which itself is the active ingredient. The boric acid diffuses into the masonry at a rate which is governed by the amount of free water available, i.e. the wetter the masonry, the faster the the movement of the sterilant into it. One ml of fused boric oxide provides as much boric acid as 3 ml of boric acid.

The dissolution of a boric oxide body can be retarded to give longer life to the body, by the inclusion of silica. Thus under conditions where the life of a paste of boric acid could be expected to be five years, the life of a fused body could be expected to be 1 2-1 5 years.

If a sterilant material more readily water soluble than boric oxide is dispersed in the form of discrete particles throughout the fused body of the boric oxide it too will diffuse only slowly because it is embedded in the less soluble boric oxide.

It is possible to use both fast and slow dissolving bodies, in different or even the same cavities, to provide a combination of the desired advantages, namely the rapid establishment of a protective environment and a very prolonged period of activity.

In the preferred form of this invention the fused bodies are homogeneous rods which are inserted into rod-shaped cavities previously drilled in the masonry.

After insertion of the fused bodies into the cavities they may be sealed therein with a cap of plastics or other suitable material. When the sterilant material has diffused through the masonry a cavity can be simply recharged by removing the cap and inserting a further fused body.

The size of shaped body used, the number of bodies used and their placement will depend on the particular environment concerned. For most uses, a cylindrical rod having a mass in the range 5 to 100, preferably 10 to 50, grams will be suitable. The diameter of such a rod can depend upon the mass since long thin rods, while having a large surface area in relation to mass, can be too fragile. A diameter of 10 to 15, especially about 12, millimetres has been found suitable.

Example 1 Holes, 9mm dia., were drilled centrally to a depth of about It + inch (3.8 cm) in standard size, i.e. 2+" x 3 7/8" x 8 5/16" (6.4 cm X 9.8 cm X 21.7 cm) plain fletton bricks. The bricks were weighed, immersed in water for 1 hour, allowed to drain on absorbent paper for 30 minutes and reweighed. The average proportion of water absorbed was about 18% by weight of bricks.

Fused boric oxide rods 8.5 mm in diameter weighing 1.1, 0.9, 0.7, 0.5 and 0.3 g were placed in the holes. Additionally one brick without any sterilant was used as a control. The holes were plugged with rubber bungs and the bricks were stored in tight-fitting plastic bags for 3 months to allow the sterilant to dissolve gradually in water and spread by diffusion to impregnate the whole brick. The bricks were then dried for 14 days in the laboratory air and two about 1 inch (2.54 cm) thick segments were cut off from the two ends of each brick. Each of the segments was cut in half so that four approx. 2+" x 1 3/4" x 1/ (6.4 cm x 4.45 cm X 2.54 cm) specimens labelled a, b, c and d were available for mycological tests.

All samples were fumigated overnight with epoxypropane vapour, ventilated with sterile air and placed on plastic mesh resting on active cultures of M. lacrymans in square sterile plastic dishes. The extent of overgrowth of the samples was assessed after 6 weeks incubation at about 20"C.

The results are given below: Table 1 Extent of Overgrowth by M. Lacrymans on Boric Oxide Treated Fletton Bricks after 6 weeks Incubation Boric oxide rod weight, g Segment Overgrowth" 1.1 a 0 b 0 c O d O 0.9 a O b 0 c O d O 0.7 a 0 b O c O d O 0.5 a + + b O c O d O 0.3 a + b ++ c ++ d 0.0 a ++++ b c d Key to all Tables: O no growth over blocks + up to 25% of both sides and top covered + + 25-50% ditto + + + 50-75% ditto + + + + 75-100% ditto The above results show that 0.7 g fused boric oxide rod per standard size fletton brick was fully effective in preventing overgrowth by the M. lacrymans fungus.

Example 2 The test was carried out exactly as above but using Ryarsh S.P. sandlime bricks. A sample of this was found to be practically free from water soluble lime, i.e. this brick is believed to be representative of well weathered mortar (fresh mortar containing free lime is known to inhibit the growth of the fungus without sterilant treatment).

The sandlime bricks were found to absorb only about 8% water; in order to ensure complete impregnation by diffusion the storage period was doubled to 6 months.

The results were: Table 11 Extent of Overgrowth by M. Lacrymans on Boric Oxide Treated Sandlime Bricks after 6 Weeks Incubation Boric oxide rod weight, g Segment Overgrowth 1.1 a 0 b 0 c O d O 0,9 a O b O c O d 0 0.7 a O b 0 c + d O 0.5 a O b c ++ d O 0.3 a + + b c ++ d 0.0 a ++++ b c d Example 3 As example 1 but using fused anhydrous octaborate, Na2B8O13, rod in the approximately equivalent weights of 1.3, 1.1, 0.9, 0.6 and 0.4 g per brick. Since this borate is much more readily soluble in water the period of diffusion was halved to 1+ months.

As expected, 0.9 g Na2B8Ot3/brick was adequate to give a complete protection against overgrowth of the fungus.

Example 4 As Example 3 but sandlime brick used and period of diffusion storage doubled to 3 months to compensate for the lower water content of the brick.

The results were similar to those recorded in Example 3.

Example 5 809 Of boric Oxide was fused with 20g silica and 8.5 mm dia. rods were cast from the melt.

Lengths of the rod corresponding to the weights of the rod used in Example 3 were used and in order to compensate for the lower rate of solublity the period of diffusion storage was quadrupled to 6 months.

The results were: Table Ill Extent of Overgrowth by M. Lacrymans on Boric Oxide/Silica Treated Fletton Bricks after 6 Weeks Incubation B2O3/SiO2 rod weight, g Segment Overgrowth 1.3 a O b O c O d O 1.1 a O b O c O d O 0.9 a + b + c O d 0 0.7 a + b + c O d ++ 0.5 a + b ++ c d 0.3 a + b c d The results were somewhat poorer than expected in that 1.1 g of the sterilant/brick was required for effective inhibition of the fungus. It is presumed that because of the lower rate of solubility of the boric oxide/silica mixture the period of diffusion should have been extended further than the 6 months allowed to ensure complete impregnation of the end sections of the brick.

Example 6 As Example 3 but the anhydrous octaborate was doped with 3% copper oxide by weight of the rod. The period of diffusion was the same, i.e. 1 + months.

The results indicated that a minimum of 0.9g rod/brick was required for effective protection against the fungus thus showing no apparent advantage over undoped anhydrous octaborate rod. However, it is to be expected that among the vast number of fungi species there will be some which will succumb more readily in the presence of the copper dopant than in its absence.

Claims (12)

1. A method of sterilising masonry in order to prevent, or reduce the incidence of, organism growth induced by the presence of moisture, which method comprises establishing in at least one cavity in the masonry a fused body of biocidal material including boric oxide, said fused body being shaped to fit said cavity.

2. A method according to claim 1 wherein the fused body consists solely of boric oxide.

3. A method according to claim 1, wherein the fused body comprises boric oxide with which another material is incorporated.

4. A method according to claim 3 in which the other material includes at least one biocide other than boric oxide or an agent which extends the spectrum of biocidal activity of boric oxide.

5. A method according to claim 3 in which the other material includes an agent which modifies the rate of release of boric oxide from the fused body under conditions of use.

6. A method according to claim 5 in which the agent is silica.

7. A method according to claim 5 in which the agent is an alkali metal oxide.

8. A method according to claim 7 wherein the fused body comprises alkali metal oxide and boric oxide in combined form as an alkali metal borate.

9. A method according to claim 8 wherein the alkali metal borate is sodium octaborate (Na2B8O13).

10. A method according to any one of the preceding claims wherein the fused body is in the form of à rod.

1 1 A method according to claim 10, wherein the fused body is in the form of a circular cylinder longer than its diameter

12. A method according to any one of the preceding claims wherein there are used both fast and slow dissolving bodies.